This invention relates to an improvement in a method and apparatus for making flexible densified polyurethane foam, and more particularly to a method and apparatus for crushing the partially cured freely risen foam.
"Crush" as used herein means to compress a cellular material so as to permanently increase the density thereof.
"Curing" as used herein means reaction of a mixture such that a permanent resilient or rigid shape is produced.
"Freely risen foam" as used herein means a foam in which expansion or "rise" due to bubble or "cell" generation has stopped yet curing has not been completed.
"Partially cured foam" as used herein means a freely risen cellular foam structure which has only cured enough that when compressed the foam is crushed yet retains a cellular structure.
"Densified foam" as used herein means foam that has been produced by crushing partially cured foam.
In U.S. Pat. No. 3,506,600, issued Apr. 14, 1970 to N. C. Zocco et al, there is disclosed a method of making densified polyurethane foam wherein the partially cured, freely risen foam is crushed between two rotating crusher rollers. After crushing between the crusher rollers, the foam is permitted to completely cure and is cut into predetermined lengths, either before or after being completely cured. The top and bottom of the foam lengths may, due to the nature of the process, have a relatively thin outer layer of very low density foam which is usually trimmed off. Then, depending upon the application, the foam length is either maintained in its original thickness, or sliced horizontally to provide a plurality of sheets from one original foam length.
Prior to the present invention, even though extensive efforts have been made to optimize the time after the foam has risen and the start of the crushing or densifying process, the density gradient across the vertical section remains significantly large. In fact, the density gradient is significantly large such that the range of densities exceed the normal product density tolerance causing more than one product to be produced when the foam length is horizontally sliced into a plurality of sheets. The economic implication of this is the production of by-product material which is either not useful or is not needed at the present time and which requires storage and necessitates an undue buildup of inventory.